1. Field of the Invention
The present invention relates to a method for manufacturing batteries, and more particularly to a method for the mass production of secondary batteries with a separating plate pressing under stable, highly controlled operating conditions.
2. Description of the Related Art
Because of the high development of consuming electronic products, such as video cameras, products of communication applications and notebook computers, toward the lighter, thinner, smaller, more economic, multifunction and portable requirements, the cost and stability of power source have become the major issues in the development and applications. As considering electrical energy, voltage and environmental protection, traditional batteries (like carbon-zinc, alkaline, mercury, or lithium batteries) are gradually replaced by the secondary batteries capable of running for longer time and charged repeatedly. Moreover, in some fields of application, like battery-powered vehicles, aircraft, microelectronic devices and wireless power supplies, secondary batteries provide broader scope for the development in the future.
Of the secondary batteries (like nickel hydride, NiH, or nickel cadmium, NiCd, batteries), the lithium polymer battery has been a required accessory in the above-mentioned high-class electronic products for its highest energy density and voltage. At present the companies like Ultralife, Valance, Moltec, Sony, Toshiba, Hitachi Maxell etc. are studying the technologies of lithium polymer battery, and most of them are making the products based on the patents of Bellcore.
In a battery, a set of components comprises the following parts: a cathodic current collector web, an anodic current collector web, a separator, a cathode, and an anode. In the manufacturing process, the cathode and anode are first pressed together with the corresponding current collector webs by hot-press rollers 112, and then a separator is added between them and hot-pressed again (or several times) to form the cell configuration. Eventually, a secondary cell is formed by a sequence of adding electrolyte, packing and activating the preformed cell configuration. Although the researches in the technology of lithium secondary battery have been lasting for a period of time, the mass production in his field is still considered not well equipped. The most important reason is that the complicated process of manufacturing and low yield rate lead to a high cost of production.
Pressing process is one of the underlying technologies currently used in making the lithium polymer battery. The object of the process is to hot-press electrodes and a separator together, and to form an anode-separator-cathode sandwich structure. The present pressing method of lithium polymer battery relies on the continuous rollers to put the electrodes and separator together. However, since the hot-pressing rollers are cylindrical in shape, the duration in pressing the electrodes and separator is short and higher pressure is required to obtain the desirable effects. On the other hand, since the substance to be pressed has to be softened enough to have effective compression, the electrodes and separator must be subject to pre-heated and thus the factor of heat conduction must be taken into account. The above two factors become a determining issue if a lithium polymer battery will be able to be pressed effectively. Under higher stress, it is easier to short-circuit the cathode and anode and thus to lose their function of current collecting. Even though short circuit does not occur, it is possible to have stress residue within batteries resulting from high level stress, and the afterward recovery process of the stress relief from the polymer will result in the expansion and then short-circuit. Oppositely, in case of insufficient press or heat energy, it will occurs that the adhesion is imperfect and the resistance of battery is so high as to deteriorate the performance of the battery.
Moreover, pressing for a short period of tine is unfavorable to cohere the interface of electrodes and separator. It is because the occurrence of desirable adhesion must be associated with the diffusion of polymer chains vibration at the interface to the interior of interface to make the chains entangled; however, for the same reason it needs sufficient time to complete the actions of diffusion and vibration, or it needs to raise the temperature of the polymers to adequately supply dynamic energy. Unfortunately, raising temperature not only consumes the power (or wastes money) but also is apt to short-circuit such soft electrode substances between the above-mentioned cathodes and anodes circuit.
In addition, for the sake of increasing the capacity of a battery, it is a must to including more layers of cells in a certain battery combination. In common method of manufacturing the battery, cells with same area are stacked with each other to achieve the above-mentioned object. However, due to the increase in the thickness of stacked components, the roller-pressing method of short time for heat conduction results to undesirable adhesion and battery features for the temperature difference between inner and outer layers of cell components. Moreover, for the purpose of getting higher capacity of battery, it is common to use cell components with a large area or in folded mode; however, the battery shape is thus limited. The current collector webs in folded mode are also easily broken around folded regions. The traditional roller-pressing method is also limited to the gauge between two rollers so as to be unfavorable to the pressing of ticker cells.
To sum up, although the present roller-pressing method posses the advantage in continuous manufacturing, there still exists a number of problems; it is unable to fulfill the requirements in secondary battery of low cost, stable quality, irregular shape and high charging capacity. Therefore, there is an urgent need to find alternatives that can react the tendency of battery industry in high efficiency, high reproducibility, and low cost.
The present invention discloses a method of producing battery with separating plate to press stacked battery components, especially a method of producing a lithium polymer battery. This method completely takes the advantage of separating plates features in flatness and isolation to overcome the problems of improper adhesion and unable to raise throughput which are met in the traditional pressing method. According to the present invention, pressing can form several layers of cell components in series or in parallel. It dose not need folding and thus avoid the occurrence of breaking. At the same time, since the cells made by the method of present invention can be worked according to a variety of requirements in size to obtain the required capacity and voltage, it keeps the features of workability and the flexibility of shape in making the battery. The manufacturing method of the present invention comprises the following steps: stacking the layers of components making secondary battery to form at least one set of cell components; adding a plurality of auxiliary layers (e.g. as buffer layers, releasing films and separating plates etc.) on each one of the first and second sides of the cell components; setting the at least two heating plates of the hot press on a default temperature; placing at least one set of the cell components and a plurality of auxiliary layers between the at least two heating plates of the hot press; pressing the at least two heating plates with the default temperature to form a cell preform from the stacked at least one set of cell components; eventually activating the cell preform into a cell and then packing cells to a battery.
In comparison with the prior art the present invention includes the following advantages:
1. The longer-duration, lower-stress pressing process is easily controlled to obtain the perfect adhesion between cell components (like anode, separator and cathode) and no short occurs. It dramatically increases the yield rate.
2. Single cell and cells in series and in parallel can be formed by designed combination, and thus dramatically reduce the time required for manufacture and increase the efficiency of production.
3. Pressing method cac press the battery with multi-layer and multi-opening in one time by the multi-opening hot press, which will achieve the object of mass production, extensive increase in the efficiency of production and the reduction of the investment in equipment. (See Table 1).
4. The use of the press with large area can produce a singe large-area cell (in series and/or parallel). The area of cell is arbitrarily determined by the size of press, such as the size of 8xe2x80x3xc2xdxc3x9711xe2x80x3 for electrical mobiles. After pressing, the cells will be able to cut into desirable size to make smaller batteries (suitable for cellular phones or palm-size computer); therefore, the size and shape of the produced battery are extremely flexible.
5. During pressing, the temperature and stress of the pressed materials are constant and stable and extensively improve the stability and yield of the productions, either for the pressing of single cells or the multi-layers/multi-opening mass pressing.
Note:
1. The number of opening of hot press is 10;
2. The number of layers per opening counted is only 14;
3. The widest width of roller pressing currently used is adapted.
4. The size of hot press is 36xe2x80x3xc3x9744xe2x80x3.
Other features and advantages of the present invention will be apparent from the accompanying drawings and from the detailed description that follows below,